SEO Reference
Canonical Tag Rules
The canonical tag is a hint, not an instruction, and that single fact explains most of the confusion around it. I use it to consolidate genuine duplicates and I use redirects or noindex when I need certainty. Here are the rules that keep implementations clean.
| Rule | Correct behaviour | Why |
|---|---|---|
| Self reference | Every indexable page points at itself | Protects against parameter duplicates |
| Absolute URLs | Use the full URL including protocol | Relative URLs are error prone |
| One tag per page | Never output two canonical tags | Google may ignore both |
| Location | In the head, or as an HTTP header | Tags injected in body are ignored |
| Consistency | Canonical, sitemap and internal links agree | Conflicting signals weaken the hint |
| Indexable target | Canonical target must be crawlable and 200 | Pointing at a redirect or 404 breaks it |
| Situation | Use | Reason |
|---|---|---|
| Page permanently moved | 301 redirect | Definitive, passes signals |
| Same content on several URLs | rel canonical | Consolidates without removing access |
| Page should not appear in search | noindex | Canonical does not remove pages |
| Tracking parameters on one page | Self referencing canonical | Stops parameter duplication |
| Paginated series | Self canonical on each page | Do not canonical page 2 to page 1 |
| Syndicated content on another domain | Cross domain canonical | Credits the original |
Notes
Canonicalising every paginated page back to page one is the mistake I see most often, and it hides the deeper items in the series from the index entirely. Each paginated page should reference itself, because the products or articles on page four exist nowhere else.
Google can and does override your canonical when the signals disagree with it. If internal links, the sitemap and the hreflang cluster all point somewhere else, Google picks the URL the site behaves as though it prefers. Search Console's page indexing report tells you which URL Google actually selected, which is the only way to confirm the hint was accepted.
Canonical does not control access or crawling. The duplicate is still reachable, still crawled and still visible to users, which is correct when the duplicate serves a purpose such as a filtered view, and wrong when you actually wanted the page gone.
Google's handling of canonicalisation and pagination guidance has changed over the years, including retiring rel next and prev support. Verify against the current Google Search Central documentation before setting a site wide rule.
Frequently asked questions
Can I canonical to a different domain?
Yes, cross domain canonicals are supported and are the right tool when your content is syndicated elsewhere. The syndicating site sets the canonical pointing at your original.
Should every page have a canonical tag?
Every indexable page should carry a self referencing canonical. It costs nothing and it protects you from tracking parameters and case variations creating duplicates.
Why is Google ignoring my canonical?
Usually because other signals contradict it, or the target is not a clean 200 page. Check the page indexing report for the Google selected canonical and align your internal links and sitemap with your intent.
Official sources
Platforms change specifications without notice. Check the primary documentation before a launch that depends on an exact value.
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